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Also are there any R complete problems? These would be the hardest decidable problems to my knowledge. Sorry if this isn't specific enough.

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PR class is associated with primitive recursive functions but not every total recursive function is a primitive recursive function. The most famous example of such functions is the Ackermann function. If you need to specify a decision problem then you can use e.g. the language $L_{A} =\{ \langle m,n,k\rangle \mid m,n,k \in \mathbb{N}, A(m,n) \le k \} \subset \{0,1\}^{*}$, (A - Ackermann function and e.g. $\langle m,n,k\rangle = 1^{m}0^{n}1^{k}$ or use any other encoding scheme). In this way you can build other examples including partial recursive functions (assuming that $\bot < 0 $) which are also not in PR. Class R is closed under $\le_{m}$ reduction but any non-trivial language in R is R-complete under this reduction so you need to use some stronger reduction to find a specific set of the hardest problems in R.

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